Synthesis, crystal structures, DNA binding and oxidative cleavage studies of copper(II) complexes of N2S2 tetradentate ligands

Two new copper(II) complexes with aminothioether ligands, [Cu(L1)(ClO4)](ClO4) · 0.5H2O (1) and [Cu(L2)(H2O)](ClO4)2 · H2O (2) (L1 = 2-benzyl-1,3-bis(aminoethylthio)propane and L2 = 2-(4-butylbenzyl)-1,3-bis(aminoethylthio)propane), have been synthesized and characterized. The single crystal X-ray diffraction analysis reveals that both 1 and 2 adopt distorted square pyramidal geometries. The binding modes of both complexes with calf thymus DNA were investigated by UV–Vis and CD spectroscopies. The results show that both complexes mainly adopt an electrostatic attraction binding mode with DNA and the binding constants are (1.62 ± 0.02) × 103 and (2.02 ± 0.02) × 103 M−1, respectively. Both complexes are able to cleave pBR322 plasmid DNA efficiently in the presence of ascorbic acid and the activity of 2 is higher than that of 1. The DNA cleavage by 1 and 2 were inhibited strongly in the presence of DMSO and tert-butyl alcohol, which suggests that hydroxyl radicals are the reactive oxygen species for the cleavage.

Graphical abstractMononuclear copper(II) complexes, [Cu(L1)(ClO4)](ClO4) · 0.5H2O (1) and [Cu(L2)(H2O)](ClO4)2 · H2O (2), with aminothioether N2S2 ligands L1 (2-benzyl-1,3-bis(aminoethylthio)propane) and L2 (2-(4-butylbenzyl)-1,3-bis(aminoethylthio)propane) have been synthesized and characterized. Both complexes exhibit efficient DNA cleavage activity in the presence of ascorbic acid and the activity of 2 is higher than that of 1.Figure optionsDownload full-size imageDownload as PowerPoint slide